1. Field of the Invention
The present application relates to a device for strapping packages.
2. Description of Related Art
In strapping machines, a package is placed on the supporting surface of a supporting table so that, in the closed position of the frame parts, it is surrounded by this frame. The tape-like strapping means, briefly called strapping tape, which has been drawn from a supply reel and is accommodated in a tape storage, is supplied via a tape drive at high speed to the tape guide channel, so that it follows the course of the channel around the package. The tape is then drawn out of the tape guide channel and tightened around the package by a tensioning drive. The loop, tightly surrounding the package, is severed from the tape supply, and the two ends of the strapping tape are joined together. According to the related art, this is done by welding, in particular by friction welding.
Such devices are known from French Patent Application 2 306 882 and European Patent 0 596 303 B1.
French Patent Application 2 306 882 describes a strapping machine having a pivoting tape guide frame divided in the center. The tape guide channel is divided into two essentially semicircular segments, which are accommodated in two frame parts and are pivotable around a pivot axis. The piston rod of a pressure cylinder acts at some distance from the pivot axis of each frame part. This pressure cylinder allows each frame part to be pivoted from a rest position, in which it is pivoted below the supporting surface for the package, into a closed position. In the closed position both frame parts are located above the supporting surface for the package. The faces of the two frame parts are in contact with one another above the package, so that a closed, essentially circular ring-shaped tape guide channel is formed. The fact that the two frame parts that form the tape guide channel can be pivoted completely below the supporting surface for the package makes it possible to move bulky or long packages in any direction on the supporting surface before or after they are wrapped with a strapping means guided through the tape guide channel. The disadvantage of this arrangement lies in that the two frame parts pivot away laterally from the supporting surface for the package. Therefore sufficient space for the two frame parts to pivot in must be available in the strapping machine. This considerably increases the size of the strapping machine, as well as the space required for it.
Another arrangement of a strapping machine is disclosed in European Patent 0 596 303 B1. Here the two frame parts are movable out of the closed position, in which they surround the package above the supporting surface, into an open position below the supporting surface, without thereby being pivoted laterally. In the closed position, the tape guide channel formed by the two frame parts is located in the strapping plane, in which the strapping tape is carried around the package. When the frame parts are lowered, they are moved downward in the vertical direction by a complex lever system, essentially translationally, and at the same time are pivoted by a specified angle, so that they open like pincers, in order to be able to be moved past the package when they are lowered. To avoid collision of the two frame parts with the machine parts, particularly the sealing unit, located in the strapping plane below the supporting surface, the frame parts are displaced transversely relative to the strapping plane in such a way that they find their rest position parallel to and alongside the machine parts located in the strapping plane. This extremely short transverse motion, necessary according to the above-mentioned document, results from the lever drive used here for the frame parts and the path of motion traversed by the frame parts. This path of motion runs along large areas below the supporting table, so that it may proceed only alongside the strapping plane with the machine parts, such as the sealing unit.
It is desirable to provide a strapping device of the said type in such a way that, for opening and closing of the frame parts, a simple drive and a simplified guide may be used for the frame parts.
According to the present invention, a strapping machine may have each frame part below a supporting surface guided moveably along its curved centerline by at least one guiding device.
According further to the present invention, a strapping machine has a guide for each frame part below the supporting surface moveable along its curved centerline, so that the closing motion and the opening motion of the frame proceed according to completely novel kinematics as compared with the related art. The frame is not pivoted about a fixed pivot axis nor is it translationally and rotationally displaced by a lever mechanism. According to the present invention, seating of each frame part alone permits its longitudinal movement in the direction of the curved centerline. A curved part moveable along a curved line is able to move on its curved path about the strapping region of the strapping machine. In other words, after placement of the package on the supporting surface, on each side of the package a frame part moves around the package by motion along a curved path, until both frame parts in the closed position form a closed tape guide channel that surrounds the package. For opening, the frame parts are moved in the opposite direction, then being guided in the guiding device following the curved centerline until each frame part is completely located below the supporting surface.
In an illustrative embodiment of the strapping machine, each frame part is curved in the shape of an arc of a circle and forms essentially a segment of a circular ring. Each frame part preferably forms just under one-half of a closed circular ring, i.e., its centerline forms an arc of approximately 170xc2x0 to 175xc2x0. Each frame part should have a tape guide channel that extends over one quarter of a circular ring (approximately 90xc2x0). Thus, a tape guide channel is arranged over approximately half the semicircular frame part. The other half of the semicircular frame part has no tape guide channel. This embodiment is advantageous especially when the two frame parts are arranged in two planes displaced with respect to one another and the portions of the tape guide channel lie on the faces of the frame parts turned toward each other, so that both portions of the tape guide channel lie in essentially the same vertical plane. For closing the tape guide channel, the semicircular frame parts must be moved 90xc2x0 in opposite directions around the center of the closed frame parts. In this closed position, the faces of the portions of the tape guide channel lie against one another, so that they form a closed tape guide channel. For opening the tape guide channel, the frame parts are again moved 90xc2x0 in opposite directions around the center of the closed frame. In the rest position, the two semicircular frame parts lie essentially alongside one another below the supporting surface. The portion of the tape guide channel being fastened to the first frame part extending over 90xc2x0 of the arc of the circular ring of this first frame part lies in the section of the second frame part having no tape guide channel and vice versa.
The guiding device for the frame parts according to the present invention may be designed in an extremely simple manner. It should consist of at least two guide rollers that lie against the first and against the second curved surface of the frame part. There the guide rollers may at the same time be designed as drive rollers and be connected with a drive motor, in particular an electric motor. In a preferred embodiment, a separate drive roller, which lies against one of the curved surfaces of the frame part, is provided in addition to the guide rollers. The drive roller alternatively may act against a non-curved surface of the frame part. Preferably, each frame part is guided in two guide-roller pairs, which at positions facing one another lie against the surfaces of the frame and are arranged close below the supporting surface on the one hand, and approximately at the center of the machine on the other hand. The two axes of the guide-roller pair near the supporting surface lie on a straight line slightly inclined with respect to the horizontal. The two axes of the rollers of the guide-roller pair in the center of the machine lie on a straight line that is inclined slightly toward the vertical. Thus, at both sides of its vertical center plane, the strapping machine in each instance comprises, for one frame part, two guide-roller pairs, which guide the frame part in the form of half a circular ring on two positions that are displaced with respect to one another by almost a quarter arc of a circle, referred to the center of the circular ring formed by the frame parts. These two guide roller pairs impart great stability to the two frame parts, while their arrangement in a machine housing may be implemented using a relatively simple design.
A drive roller, which rests against a surface of the frame part, advantageously is provided between the two guide-roller pairs that support a frame part. The drive roller advantageously rolls on the inner curved surface of the frame part. The drive roller preferably is driven by a controllable electric motor and acts via a friction coating on the surface of the frame part. The friction coating ensures that excessively high drive forces are not transmitted from the electric motor to the frame part. Depending on selection of the pressure force for the drive roller and the coefficient of friction between the friction coating of the drive roller and the frame part, the drive force for the frame part should be limited so that no persons may be injured by the moving frame part.
In addition, in order to drive the frame parts, the controllable electric motor may step through different speeds. In particular, the drive speed may be reduced shortly before closing of the frame parts by mutual contact of their front faces. This prevents a person who reaches in between the closing frame parts from being injured by too high a closing speed of the frame parts.
An interlocking drive element, for example a gear wheel, which cooperates with a gear ring, may of course be used as an alternative to a friction roller. When the drive force is to be limited here, too, a slip clutch may be provided between the drive element and the electric motor.
In an illustrative embodiment of the present invention, the tape guide channel is designed as a closed tape guide channel, i.e., in the closed state the tape guide channel is closed on all sides by essentially stationary walls. For this purpose, the portions of the tape guide channel are moveably fastened on the frame parts, so as to be moved transverse to their curved centerline, i.e., transverse to the vertical strapping plane. When the tape guide frames are closed, the two portions of the tape guide channel are shifted so that they lie in one plane. Each portion of the tape guide channel comprises a slot open on one side, which forms the recess for accommodation of the tape itself. The slot open on one side is closed off by the surface of the frame part against which the portion of the tape guide channel rests. After insertion of the strapping tape into the tape guide channel and before tightening of the strapping tape by the tensioning drive for the strapping tape, the tape guide channel is opened, in that the two portions are in each instance shifted in opposite directions transverse to the strapping plane by approximately the width of the strapping tape. At the same time the flat strapping tape, relatively rigid in its main plane, is arrested in its original position by the two parts of the frame, so that it emerges from the slot in the portion of the tape guide channel. Retraction of the strapping tape by the tensioning drive causes the formed tape loop to be tightened.
Before opening of the two frame parts that form the tape guide channel, the portions of the tape guide channel may again be moved toward the frame parts, so that they fit snugly. Transverse movement of the two portions of the tape guide channel relative to the respective frame parts to which the channel portions are fastened may be effected by any desired drive means, for example magnetic drives, pneumatic drives, control cams or lever drives.
The faces of the two parts of the frame with the tape guide channel preferably have centering means, which upon closing of the frame align the two portions of the tape guide channel to one another. Preferably, a conical bore is provided in one face of a part of the frame. A tapered pin is fastened on the face of the other part. Upon closing of the frame of the tape guide channel the faces of its two parts are moved toward one another. At the same time, the tapered pin penetrates into the conical bore. In the fully closed position the faces of the two parts of the frame are exactly aligned with one another, so that no difference in level that might hinder rapid feed and passage of the strapping tape occurs in the tape guide channel.
In order to ensure reliable operation of the strapping machine according to the present invention, a sensor preferably is provided for detection of the closed position of the two frame parts. Feed of the strapping tape is released only in the closed position. Should the frame that forms the tape guide channel be prevented from closing completely in its path of motion, either by the package or by some other obstacle, tape feed is halted. This ensures that tape feed into the tape guide channel takes place only when the tape guide channel is properly closed.
In addition to the limitation of the driving force of the frame parts via a slip clutch, described above, it is likewise possible to increase personal safety via a sensor for determination of the driving force acting on the frame parts. Should the sensor measure too high a driving force, for example when a frame part strikes an obstacle before the closed position, the power supply to the drive device for the frame parts may be interrupted.
An embodiment of the strapping machine may have two semicircular frame parts in two different planes, where the portions of the tape guide channel on the faces of the frame parts facing one another are arranged in essentially the same plane, preferably is fastened to a supporting frame that has the cross section of an upside-down xe2x80x9cU.xe2x80x9d The supporting frame consists of two vertical cheeks facing one another and a bearing surface running between these cheeks. The machine parts of the strapping machine, in particular the sealing unit, the tape drive and the guide elements that introduce the tape delivered from the tape storage near the supporting surface into the tape guide channel, as well as the tensioning drive, are arranged on the bearing surface.
A frame part for formation of the tape guide channel is preferably fastened to each cheek of the supporting frame. For this purpose the cheek supports the two guide-roller pairs as well as the drive motor with the drive roller for the respective frame part. Preferably, identical structural parts are used for the two cheeks, and identical guide-roller pairs and drive motors for the two frame parts may likewise be used. In this way, the number of parts that have to be fabricated for production of the strapping machine is considerably reduced.
The surfaces of the frame parts as well as the rollers rolling on them are preferably designed arched in complementary fashion, so that the frame parts are stabilized in the transverse direction by the rollers fastened to the supporting frame of the machine.
Individual features of the present invention may of course be varied without departing from the scope of the disclosure and the claims. Thus, it is not absolutely necessary that the frame parts have an exactly annular segment-like shape. The curvature may alternatively differ from a circular curvature, while it must be noted that unbalanced forces are observed during closing and opening of the frame parts. The guiding devices for the frame parts must be designed appropriately strengthened. In the case of frame parts that are not exactly circular in shape, it will as a rule also be necessary to fasten individual guide rollers moveably, e.g., pretensioned by a spring force, to the supporting frame of the machine, since the surface sections which rest against the guide rollers will lie at the same position only during motion of a circular frame part.